Local Anesthetics - Flood
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Questions and Answers

How do local anesthetics reduce excitability of neuronal, cardiac, or central nervous system tissue?

  • By blocking Na1 current through voltage-gated channels (correct)
  • By altering the resting transmembrane potential
  • By enhancing the transmission of nerve impulses
  • By increasing the rate of depolarization
  • Which part of the sodium channel serves as a specific receptor for local anesthetic molecules?

  • b subunit
  • a subunit (correct)
  • DI subunit
  • DII subunit
  • What happens when sodium ion channel permeability fails to increase?

  • An action potential is propagated
  • The rate of depolarization speeds up
  • Threshold potential is not reached (correct)
  • Threshold potential is reached more quickly
  • How do local anesthetics affect the transmission of nerve impulses?

    <p>By inhibiting passage of sodium ions through selective channels</p> Signup and view all the answers

    What is the role of the b subunits in the sodium channel?

    <p>Forming the large sodium-conducting pore</p> Signup and view all the answers

    How many distinct functional subtypes of voltage-gated Na1 channels are recognized based on their pore-forming a subunits?

    <p>Nine</p> Signup and view all the answers

    Which subunit of the sodium ion channel allows for ion conduction and binds to local anesthetics?

    <p>The a subunit</p> Signup and view all the answers

    How do the binding affinities of local anesthetics to sodium ion channels depend?

    <p>They depend on the conformational state of the sodium channel</p> Signup and view all the answers

    Which state of the sodium channel do local anesthetics preferentially bind to?

    <p>The inactivated-closed state</p> Signup and view all the answers

    What is the mechanism by which local anesthetics prevent the conduction of nerve impulses?

    <p>They stabilize sodium channels in the inactivated-closed state</p> Signup and view all the answers

    How do local anesthetics gain access to their receptors on sodium channels?

    <p>They can only access the receptors when the channels are in the activated-open state</p> Signup and view all the answers

    What is the relationship between the frequency of nerve stimulation and the conduction blockade induced by local anesthetics?

    <p>Higher frequency of nerve stimulation increases the conduction blockade</p> Signup and view all the answers

    Which type of ion channel, in addition to sodium channels, are also blocked by local anesthetics?

    <p>Both calcium and potassium ion channels</p> Signup and view all the answers

    What is the term used to describe the minimum concentration of a local anesthetic required to produce conduction blockade of nerve impulses?

    <p>Cm</p> Signup and view all the answers

    How does an increased tissue pH affect the Cm (minimum concentration) of a local anesthetic?

    <p>Increased pH decreases the Cm</p> Signup and view all the answers

    How does nerve fiber diameter affect the Cm (minimum concentration) of a local anesthetic?

    <p>Larger nerve fibers require higher concentrations of local anesthetic for conduction blockade</p> Signup and view all the answers

    Which factor is MOST important in the redistribution of local anesthetics after rapid initial uptake into the lungs?

    <p>Lipid solubility</p> Signup and view all the answers

    Which of the following patient-related factors LEAST influences the absorption and plasma concentrations of local anesthetics?

    <p>Renal function</p> Signup and view all the answers

    What is the primary mechanism by which the lungs limit the concentration of local anesthetics that reach the systemic circulation?

    <p>Pulmonary extraction of the local anesthetic</p> Signup and view all the answers

    Which of the following is the MAIN reason that clearance values and elimination half-times for amide local anesthetics represent mainly hepatic metabolism?

    <p>Reduced renal excretion of unchanged drug</p> Signup and view all the answers

    Which of the following is the LEAST important step in the complete metabolism of amide local anesthetics?

    <p>Formation of a cyclic aniline derivative</p> Signup and view all the answers

    Which of the following is the MAIN reason that sustained increases in plasma concentrations and systemic toxicity are more likely with amide local anesthetics compared to ester local anesthetics?

    <p>Slower metabolism of amide local anesthetics</p> Signup and view all the answers

    Which of the following is the LEAST likely way that propranolol can influence the pharmacokinetics of local anesthetics?

    <p>Increasing renal excretion</p> Signup and view all the answers

    Which of the following is the MAIN reason that pharmacokinetic studies of ester local anesthetics are limited?

    <p>Rapid hydrolysis in the plasma and liver</p> Signup and view all the answers

    Which of the following amide local anesthetics undergoes the SLOWEST metabolism?

    <p>Bupivacaine</p> Signup and view all the answers

    What is the MAIN reason that renal excretion of unchanged local anesthetics is usually less than 5%?

    <p>Poor water solubility of the drugs</p> Signup and view all the answers

    What is the purpose of adding 1 mL of 8.4% sodium bicarbonate to 30 mL of chloroprocaine solution before placing it into the epidural space?

    <p>To increase the efficacy of the chloroprocaine-bupivacaine combination</p> Signup and view all the answers

    What is the primary reason for adding epinephrine to a local anesthetic solution?

    <p>To prolong the duration of conduction blockade and decrease systemic absorption</p> Signup and view all the answers

    What is the effect of adding epinephrine to bupivacaine or etidocaine solutions compared to adding it to lidocaine solutions?

    <p>The impact of epinephrine is less for bupivacaine and etidocaine</p> Signup and view all the answers

    What is the effect of adding epinephrine to a low dose of tetracaine (6 mg) for spinal anesthesia?

    <p>It increases the success rate of spinal anesthesia</p> Signup and view all the answers

    What is the effect of adding epinephrine to local anesthetic solutions on the onset rate of local anesthesia?

    <p>It has little to no effect on the onset rate of local anesthesia</p> Signup and view all the answers

    What is the effect of adding epinephrine to local anesthetic solutions on the likelihood of systemic toxicity?

    <p>It decreases the likelihood of systemic toxicity</p> Signup and view all the answers

    What is the potential adverse effect of administering local anesthetic solutions containing epinephrine in the presence of inhaled anesthetics?

    <p>It can enhance cardiac irritability</p> Signup and view all the answers

    What are the two principal side effects related to the use of local anesthetics?

    <p>Allergic reactions and systemic toxicity due to excessive plasma and tissue concentrations</p> Signup and view all the answers

    What is the impact of adding epinephrine to the local anesthetic solution influenced by?

    <p>The specific local anesthetic selected and the level of sensory blockade required</p> Signup and view all the answers

    What is the effect of adding epinephrine or phenylephrine to bupivacaine or lidocaine placed into the subarachnoid space?

    <p>It extends the duration of sensory anesthesia in the lower extremities</p> Signup and view all the answers

    What is the estimated rate of systemic toxicity resulting in seizures with the use of local anesthetics?

    <p>1 to 4 per 1,000 patient exposures</p> Signup and view all the answers

    Which local anesthetic is the drug most likely to be associated with systemic toxicity resulting in seizures?

    <p>Bupivacaine</p> Signup and view all the answers

    What percentage of adverse reactions to local anesthetics are due to an allergic mechanism?

    <p>Less than 1%</p> Signup and view all the answers

    Which class of local anesthetics is more likely to evoke an allergic reaction?

    <p>Ester local anesthetics</p> Signup and view all the answers

    What is the primary cause of reactions that are often attributed to an allergic reaction to local anesthetics?

    <p>Excess plasma concentrations of the local anesthetic</p> Signup and view all the answers

    What is the basis for cross-sensitivity between different classes of local anesthetics?

    <p>There is no cross-sensitivity between classes of local anesthetics</p> Signup and view all the answers

    Which local anesthetic has the highest rate of hydrolysis by plasma cholinesterase?

    <p>Chloroprocaine</p> Signup and view all the answers

    Which local anesthetic is the most slowly eliminated of all the amide derivatives?

    <p>Dibucaine</p> Signup and view all the answers

    Which local anesthetic is metabolized in the liver and is highly bound to a1-acid glycoprotein?

    <p>Dibucaine</p> Signup and view all the answers

    Which enzyme is inhibited by dibucaine, leading to prolonged effects and toxicity of certain drugs?

    <p>Plasma butyrylcholinesterase</p> Signup and view all the answers

    Which local anesthetic has its metabolism facilitated by measurement of the degree of enzyme suppression by dibucaine?

    <p>Procaine</p> Signup and view all the answers

    Which local anesthetic has an elimination half-time shorter than bupivacaine?

    <p>Ropivacaine</p> Signup and view all the answers

    What is the antigen responsible for subsequent allergic reactions to ester local anesthetics?

    <p>Paraaminobenzoic acid</p> Signup and view all the answers

    Which local anesthetic undergoes hydrolysis in the liver rather than in the plasma?

    <p>Cocaine</p> Signup and view all the answers

    What is a test termed that evaluates patients suspected of having atypical pseudocholinesterase by measuring the degree of enzyme suppression by dibucaine?

    <p>Dibucaine number test</p> Signup and view all the answers

    Which local anesthetic has an intermediate lipid solubility between lidocaine and bupivacaine?

    <p>Ropivacaine</p> Signup and view all the answers

    What is the advantage of benzocaine being a weak acid (pKa 3.5)?

    <p>It is ideal for topical anesthesia of mucous membranes.</p> Signup and view all the answers

    What is a potential life-threatening complication associated with benzocaine?

    <p>Methemoglobinemia</p> Signup and view all the answers

    How does alkalinization of local anesthetic solutions affect the onset of neural blockade?

    <p>It shortens the onset of neural blockade.</p> Signup and view all the answers

    Which substance has shown promising results when added to the intrathecal space along with local anesthetic?

    <p>Dexmedetomidine</p> Signup and view all the answers

    What does the combination of local anesthetics using chloroprocaine and bupivacaine aim to achieve?

    <p>Rapid onset and prolonged duration of action</p> Signup and view all the answers

    What is a common method used to speed up the onset of peripheral nerve block and epidural block?

    <p>Alkalinization with sodium bicarbonate</p> Signup and view all the answers

    Why is cocaine present in urine for 24 to 36 hours?

    <p>Related to excretion of water-soluble metabolites</p> Signup and view all the answers

    What effect does dexmedetomidine have when used as an adjuvant in local anesthetic mixtures?

    <p>Increased duration of sensory block</p> Signup and view all the answers

    Which of the following statements about lidocaine is correct?

    <p>Monoethylglycinexylidide has approximately 80% of the cardiac antidysrhythmic activity of lidocaine.</p> Signup and view all the answers

    What is the primary concern with the use of prilocaine?

    <p>It can lead to potentially life-threatening methemoglobinemia.</p> Signup and view all the answers

    Which of the following statements about mepivacaine is true?

    <p>Mepivacaine lacks vasodilator activity, making it suitable when epinephrine is not recommended.</p> Signup and view all the answers

    What is the primary metabolite of bupivacaine that has been measured in blood or urine?

    <p>N-desbutylbupivacaine</p> Signup and view all the answers

    Which of the following statements about ropivacaine is true?

    <p>Only a small fraction of ropivacaine is excreted unchanged in the urine when the liver is functioning normally.</p> Signup and view all the answers

    What is the primary plasma protein-binding site for bupivacaine?

    <p>$\alpha_1$-acid glycoprotein</p> Signup and view all the answers

    Which of the following factors can increase the concentration of $\alpha_1$-acid glycoprotein, the primary plasma protein-binding site for bupivacaine?

    <p>Postoperative trauma</p> Signup and view all the answers

    Which of the following statements about maternal clearance of lidocaine is true?

    <p>Maternal clearance of lidocaine is decreased in the presence of pregnancy-induced hypertension.</p> Signup and view all the answers

    What is the primary mechanism by which prilocaine causes methemoglobinemia?

    <p>The metabolite orthotoluidine oxidizes hemoglobin to methemoglobin.</p> Signup and view all the answers

    Which of the following statements about the metabolism of bupivacaine is true?

    <p>The mean total urinary excretion of bupivacaine and its dealkylation and hydroxylation metabolites accounts for less than 40% of the total anesthetic dose.</p> Signup and view all the answers

    Which of the following statements about the minimum length of myelinated nerve fiber required for conduction blockade is correct?

    <p>At least two successive nodes of Ranvier (approximately 1 cm) must be exposed to an adequate concentration of local anesthetic for conduction blockade to occur in an A fiber.</p> Signup and view all the answers

    Which of the following statements about the differential conduction blockade of nerve fibers by local anesthetics is correct?

    <p>Preganglionic B fibers are more readily blocked by local anesthetics than any other fiber, even though they are myelinated.</p> Signup and view all the answers

    Which statement best describes the effect of pH on the ionization of local anesthetics?

    <p>Local anesthetics are weak bases, so an acidic environment increases the ionized fraction of the drug.</p> Signup and view all the answers

    Which of the following factors influences the apparent potency and duration of action of local anesthetics?

    <p>The intrinsic vasodilator activity of the local anesthetic.</p> Signup and view all the answers

    Which of the following statements best explains why lidocaine has a shorter duration of action compared to mepivacaine?

    <p>The enhanced vasodilator action of lidocaine compared with mepivacaine results in greater systemic absorption and shorter duration of action of lidocaine.</p> Signup and view all the answers

    Which of the following statements best explains the occasional prolonged sensory blockade observed after injection of etidocaine?

    <p>The greater lipid solubility of etidocaine results in tissue sequestration and less available drug for systemic absorption.</p> Signup and view all the answers

    Which of the following statements regarding the absorption of local anesthetics into the systemic circulation is correct?

    <p>The ultimate plasma concentration of a local anesthetic is determined by the rate of tissue distribution and the rate of clearance of the drug.</p> Signup and view all the answers

    Which of the following statements regarding the differential conduction blockade of nerve fibers by local anesthetics is correct?

    <p>Slightly higher concentrations of local anesthetics interrupt conduction in small C fibers and small- and medium-sized A fibers, with loss of sensation for pain and temperature, while touch, proprioception, and motor function are still present.</p> Signup and view all the answers

    Which of the following statements regarding the effect of tissue infection on local anesthesia is correct?

    <p>Acidosis present in tissue infection increases the ionized fraction of local anesthetics, resulting in poorer quality of local anesthesia.</p> Signup and view all the answers

    What term is used to describe the anesthesia produced by the IV injection of a local anesthetic solution into an extremity isolated from the rest of the systemic circulation by a tourniquet?

    <p>Intravenous regional anesthesia</p> Signup and view all the answers

    Which drug, when used as an additive to local anesthetic solutions for peripheral nerve blocks, is associated with significant adverse effects and therefore cannot be routinely recommended?

    <p>Ketamine</p> Signup and view all the answers

    What is the determining factor for the duration of anesthesia in IV regional anesthesia where a local anesthetic solution is injected into an extremity isolated by a tourniquet?

    <p>Length of time the tourniquet is kept inflated</p> Signup and view all the answers

    Which local anesthetic is most frequently chosen for producing IV regional anesthesia?

    <p>Lidocaine</p> Signup and view all the answers

    Which amide local anesthetic provided superior analgesia compared to lidocaine when utilized for IV regional anesthesia?

    <p>Mepivacaine</p> Signup and view all the answers

    What effect does the release of a tourniquet have on normal sensation and skeletal muscle tone in IV regional anesthesia?

    <p>It allows immediate return of normal sensation and muscle tone</p> Signup and view all the answers

    Which local anesthetics produce satisfactory effects when used for IV regional anesthesia?

    <p>Both ester and amide local anesthetics</p> Signup and view all the answers

    For IV regional anesthesia, what do lower plasma concentrations of prilocaine compared to lidocaine after tourniquet deflation indicate?

    <p>'Prilocaine has a greater margin of safety than lidocaine.'</p> Signup and view all the answers

    What does the duration of anesthesia in IV regional anesthesia depend on?

    <p>The length of time the tourniquet is kept inflated</p> Signup and view all the answers

    What characteristic distinguishes intravenous regional anesthesia from other types of anesthesia techniques?

    <p>Intravenous regional anesthesia isolates the extremity from systemic circulation with a tourniquet.</p> Signup and view all the answers

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